Recently, it has been proposed to use light emitting diodes (LEDs) as light sources in a projection-type display device. In particular, in a digital-light-processing (DLP; registered trademark)-type display device using a digital-micromirror-device, LEDs emitting a red light beam (hereinafter, also referred to as R-LEDs), LEDs emitting a green light beam (hereinafter, also referred to as G-LEDs), and LEDs emitting a blue light beam (hereinafter, also referred to as B-LEDs) are used, and the LEDs of three colors are turned on sequentially (see Patent Document 1). In such a projection-type display device, a driving circuit for a light source is provided for each emission color of the light source. More specifically, three constant current circuits consisting of a constant current circuit for R-LEDs, a constant current circuit for G-LEDs, and a constant current circuit for B-LEDs are provided correspondingly to emission colors of LEDs.
In the above-mentioned display device, input video signals are converted into pieces of digital data of respective colors, that is, red data (hereinafter, also referred to as R data), green data (hereinafter, also referred to as G data), and blue data (hereinafter, also referred to as B data), and the DMD is driven in accordance with the pieces of data of the respective colors, to thereby perform intensity modulation on the light beams of three colors. That is, a red light beam is subjected to intensity modulation in accordance with the R data, a green light beam is subjected to intensity modulation in accordance with the G data, and a blue light beam is subjected to intensity modulation in accordance with the B data. The light beams of three colors subjected to intensity modulation are projected onto a screen or the like through a projection lens, so that video images are displayed.